lkml.org 
[lkml]   [2019]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Re: [PATCH V3] MIPS: Add get_thread_area syscall
Dear Paul,

Thank you very much.
I didn`t know this way asm("rdhwr %0, $29" : "=r"(*ptls)) before.Now I have a test for it and it realy can work normally.
I just find get_thread_area syscall at path arch/x86.so I have a implement on MIPS platform. And I think set_thread_area and get_thread_area is matched in pairs.
Now it seems that the get_thread_area syscall is not necessary for criu.

Thanks,
Guoyun Sun

> -----原始邮件-----
&gt; 发件人: "Paul Burton" <paulburton@kernel.org>
&gt; 发送时间: 2019-12-17 03:33:33 (星期二)
&gt; 收件人: "Guoyun Sun" <sunguoyun@loongson.cn>
&gt; 抄送: "Ralf Baechle" <ralf@linux-mips.org>, "James Hogan" <jhogan@kernel.org>, "Peter Zijlstra" <peterz@infradead.org>, "Christian Brauner" <christian.brauner@ubuntu.com>, "Arnd Bergmann" <arnd@arndb.de>, "Heiko Carstens" <heiko.carstens@de.ibm.com>, "David Howells" <dhowells@redhat.com>, "Geert Uytterhoeven" <geert@linux-m68k.org>, "Catalin Marinas" <catalin.marinas@arm.com>, linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, "Tiezhu Yang" <yangtiezhu@loongson.cn>, "Xuefeng Li" <lixuefeng@loongson.cn>
&gt; 主题: Re: [PATCH V3] MIPS: Add get_thread_area syscall
&gt;
&gt; Hi Guoyun,
&gt;
&gt; On Mon, Dec 16, 2019 at 10:17:51AM +0800, Guoyun Sun wrote:
&gt; &gt; CRIU(https://criu.org/) tools will dump TLS(Thread Local Storage) by
&gt; &gt; get_thread_area during checkpoint and restore TLS by set_thread_area during
&gt; &gt; restore. without this syscall, criu restore will fail on MIPS platform
&gt; &gt; because a variable with GCC __thread will be invalid.
&gt; &gt;
&gt; &gt; The following function will be called when criu restore
&gt; &gt;
&gt; &gt; static inline void restore_tls(tls_t *ptls) {
&gt; &gt; asm volatile(
&gt; &gt; "move $4, %0 \n"
&gt; &gt; "li $2, "__stringify(__NR_set_thread_area)" \n"
&gt; &gt; "syscall \n"
&gt; &gt; :
&gt; &gt; : "r"(*ptls)
&gt; &gt; : "$4","$2","memory");
&gt; &gt;
&gt; &gt; the *ptls can be obtained by get_thread_area on MIPS platform when criu
&gt; &gt; checkpoint. just like this:
&gt; &gt;
&gt; &gt; static inline void arch_get_tls(tls_t *ptls)
&gt; &gt; {
&gt; &gt; asm volatile(
&gt; &gt; "move $4, %0 \n"
&gt; &gt; "li $2, "__stringify(__NR_get_thread_area)" \n"
&gt; &gt; "syscall \n"
&gt; &gt; :
&gt; &gt; : "r"(ptls)
&gt; &gt; : "$4","$2","memory");
&gt; &gt;
&gt; &gt; }
&gt;
&gt; Why would you need a syscall for this?
&gt;
&gt; Why not retrieve the value using the rdhwr instruction just like every
&gt; other bit of code using thread-local storage does?
&gt;
&gt; ie. something like:
&gt;
&gt; static inline void arch_get_tls(tls_t *ptls)
&gt; {
&gt; asm("rdhwr %0, $29" : "=r"(*ptls));
&gt; }
&gt;
&gt; Thanks,
&gt; Paul
</lixuefeng@loongson.cn></yangtiezhu@loongson.cn></catalin.marinas@arm.com></geert@linux-m68k.org></dhowells@redhat.com></heiko.carstens@de.ibm.com></arnd@arndb.de></christian.brauner@ubuntu.com></peterz@infradead.org></jhogan@kernel.org></ralf@linux-mips.org></sunguoyun@loongson.cn></paulburton@kernel.org>
\
 
 \ /
  Last update: 2019-12-17 02:48    [W:0.033 / U:1.204 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site